The traditional implantable cardiac pacemaker includes a pulse generator device to which one or more flexible elongate lead wires are coupled. The device is typically implanted in a subcutaneous pocket, remote from the heart, and each of the one or more lead wires extends therefrom to a corresponding electrode that is positioned at a pacing site, either endocardial or epicardial. Mechanical complications and/or MRI compatibility issues, which are sometimes associated with elongate lead wires, have motivated the development of implantable cardiac pacing devices that are wholly contained within a relatively compact package for implant in close proximity to the pacing site, for example, within the right ventricle RV of the heart. With reference to FIGS. 1A-B, such a device 200 is illustrated, wherein an hermetically sealed housing 205, preferably formed from a biocompatible and biostable metal such as titanium, contains a pulse generator, or an electronic controller (not shown), to which at least one electrode 211 is coupled, for example, by a hermetic feedthrough assembly (not shown) known to those skilled in the art of implantable medical devices. Housing 205 may be overlaid with an insulative layer, for example, medical grade polyurethane, parylene, or silicone.
FIG. 1A illustrates device 200 implanted at a target site 150 in the apex of the right ventricle RV, for example, being fixed in place by a fixation member 215 that includes a plurality of tines, which are better seen in FIG. 1B. Embodiments of the illustrated fixation member 215 are described in commonly assigned U.S. Patent application 2012/0172690, which is hereby incorporated by reference in its entirety. FIG. 1A further illustrates device 200 having been deployed out from a distal portion of an elongate delivery tool 100, for example, a guiding catheter, which has been maneuvered up through the inferior vena cava IVC and into the right ventricle RV from the right atrium RA, according to methods known in the art of interventional cardiology.
FIGS. 2A-B are plan views of a specialized tool 300 developed for the deployment of relatively compact implantable medical devices like device 200, in lieu of more common catheter-type tools, like tool 100. FIGS. 2A-B illustrate tool 300 including a handle assembly 310, an outer tube 330, and a core 350, for example, an inner elongate tube (shown with dashed lines in FIG. 2A), extending within outer tube 330. FIGS. 2A-B further illustrate outer tube 330 including a distal-most portion 332, which is sized to contain an implantable medical device, for example, the above-described device 200, which can be seen in the cut-away section of FIG. 2B, when a proximal end of the device, for example, attachment structure 222, abuts a distal member 352 of core/tube 350. Distal-most portion 332 also defines a distal opening 303 of outer tube 330, through which device 200 is deployed, for example, as shown in FIG. 2B, when outer tube 330 is withdrawn, or retracted, relative to core/tube 350, per arrow b, for example, by moving a control member 312 of handle assembly 310 per arrow B. With further reference to FIGS. 2A-B, handle assembly 310 includes another control member 311 to which a proximal end of a pull wire (not shown) may be attached; a distal end of the pull wire may be anchored adjacent to distal member 352 of core/tube 350, so that when control member 311 is moved per arrow A tool 300 is deflected per arrow a, as shown in FIG. 2B. The deflection, per arrow a, may be useful to position distal-most portion 332 in close proximity to target site 150 so that, upon retraction of outer tube 330, per arrow b, the aforementioned tines of fixation member 215 may engage with the tissue at site 150. Disclosure included in commonly assigned United States Patent Application 2013/0103047, which describes a general construction of a tool like tool 300, is hereby incorporated by reference.
With reference back to FIG. 1A a tether 140 is shown extending from an attachment structure 222 of device 200 and back into tool 100, so that a proximal portion of tether 140, which extends out from a proximal end of tool 100, is accessible to an operator. With reference to FIG. 1B, attachment structure 222 includes an eyelet 202 through which tether 140 may be looped to temporarily secure device 200 to tether 140. Tether 140 may similarly be secured to device 200, when device 200 is loaded in tool 300 for deployment. With reference to FIGS. 2A-B, the looped tether 140 extends within core/tube 350 so that ends of tether 140 extend from a proximal opening 351 of core 350, where the operator may tug on tether 140 to test the fixation of device 200 at the implant site, and, if necessary, apply a greater force to tether 140 to remove device 200 from the implant site for repositioning at a more suitable site. If the operator is satisfied with the performance of device 200 at the illustrated implant site, the operator may release tether 140 from attachment structure 222 and withdraw tether 140 through delivery tool 300.